Bob weight for balance testing of counterbalanced crankshaft



May 26, 19 59 I c. w. M MILLAN BOB WEIGHT FOR BALANCE TESTiNG OF COUNTERBALANCED CRANKSHA Filed Jan. 10. 1958 El /n. V... v f

I NVENHTOR CHARLES W. MACMIITLAN' ATTYS.

,r I BOB WEIGHT non BALANCE TESTINGOF: COUNTERBALANCED Charles w. o

Manufacturing Company, tionof Delaware Rq slant 11-. a am uf- 1' Application January 16, i958, Serial N f7o8,121

ancetestingmachine.

The usual crankshaft. ota lengine is constructed with pennanentcounterweights ,to-counterect the cen- MacMillan,,kockflslaui llllliassigniir o ps trifugal forces set up by the piston and rod assembly.

Consequently, when rotating the crankshaft without :the piston and rodassembly connected :thereto as when the crankshaft alone is rotated in aconventional balance testing machine, the permanent counterweights induce a centrifugal force tive of .the actual .Workingconditions of the crankshaft. Accordingly, when testing the balance of such. a crankshaft,, it is necessary tocompensate forthe loss of the piston and rod assembly, by supplying dummy weights or so-called bobweights to I sentative and equivalent to the absent .piston and, red as} semblyin so far as,their contributions ,to the. forces-of thesystem are concerned. 1 One of theimportant features gof. the present invention on the-crankshaftwhich is not representathe crankshaft whichare repreresides in theprovision of a .bob weight which, is of-simthe provision of a bob weight which is constructed in identical halves whereby the halves constructed in largequantity. M

Qther-features-and advantages of the preseritinvention l maybe econom cally willf be apparent from the following-detailed description. Q1 1 the aw g I 1 is a fragmentary prspectlv viewof "a' V--8 crankshaft carrying bobweights comprising the embodiment of the present inventio Fig. 2 is a sectional view through a crankshaft crankpin illustrating the application of the bob weight to the crankpm.

Fig. 3 is a top plan view of the improved bob weight.

Fig. 4 is an exploded view of the bob weight illustrating the component parts thereof.

Referring in detail to the drawing, 1 indicates a fragmentary portion of a crankshaft for an eight cylinder V-type internal combustion engine. The crankshaft 1 comprises portions 2 which seat in the main bearings of the engine (not shown) and constitute the axis about which the crankshaft revolves. Crankpins 3, one only of which is illustrated, are radially offset from the axis of the portions 2 and constitute the pins upon which the connecting rod bearings (not shown) are secured.

To counterbalance the rotating weights of the piston rod assemblies during operation, counterweights 4 comprise a portion of the crankshaft 1, said counterweights having their centers of gravity substantially diametrically offset from the crankpins 3. Thus, during operation of the engine, the crankshaft is intended to be balanced.

, To secure the 513013: weight crankpinrvidedvwith a bore, (not shown) I=tapered block 9 is 1 provided @with a :shown) which is axial 1 alignment with:v the tbore =,;in

Conventional balance testing machines" cannot determine the condition of balance. of a crankshafhwith the piston rod assembly secured thereto. Therefore, Weights equivalent, in so fares the r otationaljforces 'are concerned, to the piston. rod assembly: to be used are applied to thecranksh aftc Such dummy are secured to the crankpins 3. I H The weight of a predetermined, dummy weight, tape applied to a predetermined .crankpin is dependent upon the weight characteristics of the piston, rod ,assenibly fto be; applied to saidcrankpim :1 In .determiningthe weight of. the dummy weight, the entire connecting irod the rotating end of the connecting rod including, itsbearing, and the piston, ringsand pistonpin are separately, aeeu; .rately weighed. Empirieally, .100 .percent of the weight of the. rotating-portion of the .endof the connecting rod and piston assembly is addedtoSOpercent of th elweight .of, the; reciprocating portion thereof to arrive; at the dummy weight required.- .1 l; In order, therefore, properly; to: couditionqthe crankshaft 1 fora balancing testa dummy weightonbob weight 5 is mountednpon each .crankpinfi. The,.bob ;we ight 5 1c mpr s s Q nt halflp r n ,6 d .Eaahhalf portion comprisesa yoke 8 w ch. includes ,apairof .tapered blocks 9 and .9 and a joining block .10.,rigidly securingthetapered blocks together. The. tapered block 9..-of eachhalf-portion 6 and 7, carries a;pair of spaced dowel pins '1 1 =a nd each-taperedblock 9 is provided with spaced openings 12 into. which therespective dowel, pins 11..slidably fit; 4:. ,A' screw shank 13 isgcarried by each joining-block 10 and extends transversely tosaid blocks. A knurled .wheel .14 and a boss-.15 carried, thereby are provided-with an internally threaded borell 6 whereby ;sa1d knurled, wheel .engages with each screw-13. .A'plurality ofrcentrally apertured discs17 areemployed as variable weights and are adapted to be carried upon each screw 13,.saidweights being confined between the bosses :and the-respective :joiningblocks10.1w: ,3;1:.the

,respective half-portionsnG and 7. are positionedfton opposite sides ofthe .crankpin, with the tapered surfaces-0f :the blocks .9 and=9.-in:tangential-linecontact withL-the surface of the crankpim: ;Block 9 of 1 each half-:isi-;pro through v. which ;.-:the threaded shank of a cap screw 18. freely extendst Each threaded bore :=.(not

the companion tapered block 9, when the blocks are iustaposed, whereby the cap screw may threadedly engage with the aperture in block 9 to secure the bob weight upon the crankpin 3.

As hereinbefore described, the companion half-portions 6 and 7 of the bob weight 5 are identical and they are, including dowels 11, wheels 14, screws 18 and 13 and blocks 9, 9' and 10, equal in weight, and when the bob weight 5 is secured to the crankpin 3, there will be equal numbers of discs on each half-portion.

Of course, for a predetermined piston rod assembly, a predetermined number of pairs of discs will be used. For piston rod assemblies of ditferent weights, pairs of discs will be added or removed in order that the bob weight as a whole will conform with the weight characteristics of the piston rod assembly.

By the provision of the tapered surfaces upon the blocks 9 and 9', the bob weight has application to crankpins of a large range of diiferent diameters and, hence, only a limited number of bob weights need be stocked. In addition, by the provision of the easily applied and removed disc weights 17 the bob weight embodying the present invention may be quickly and conveniently adaptedto"supplantor'be a weight substitute for many piston rod assemblies having difierent weight characteristics;

Many non-inventive variations of the present invention may be devised by .any oneskilled in theart and, hence, it; is 'notintended that the present invention he limited. to the eiiact"details "shown anddescribed,"except as necessitated by the appended claims.

"*1 claim asm'y invention: I 1."'Ab ob weight"for'counterbalanced crankshafts of V type eight cylinder internal combustion engines, which comprises, a pair of substantiallyidentical half-portions forembracingfopposite-sides of a crankshaft crankpin, each half-portion "comprising a yokehaving opposed opp'osfit'ely inclined: contact surfaces'for contacting thecrank pin at" circumferentiallyispaced portions ther'eoffsecuring ineans carried by "each oppositeyoke for engaging the other 'y'oke toseiiuresaid yokes together and in diametri- 'c'all'y opposite-positions on saidcrankpin, aligning means carried ""by 'eachyoke slidably engageable with the opposedyoke for--preventingrelative lateral movement of said'yokes, means carried by eachyoke for holding incrementalweights uponthe respective yokes, and-securing means carried by said holding means for immovably securing-said incremental'weights to the respective yokes. lt-fl bob weight for counterbalanced crankshafts of N type "eight cylinder-internal combustion engines, which comprises, a pair of substantially identical half-portions forembr'acing'opposite sides of a crankshaft crankpin, each-halfportion-comprising 'a yoke having spaced opposed oppositely inclined contact surfaces for contacting the crankpinatbircriniferentially spaced portions thereof, securing means 'carried'by each-opposite yoke for engaging 'th'eiotheryoke-to secure said yokes together and in-"diametrically opposite positions on said crankpin, dowel pins carried by each yoke slidablyengageable' in receiving=apei tures in the opposed yoke forpreventing relative lateral movement of said yokes, means carried by each yoke= for holding incremental weights upon the respective yekes, and securing means carried by said holding means for immovably securin'g said incrementalweights to the respective :yokes.

-bob weightfor counterbalanced crankshafts of V-type eight cylinder internal combustion engines, which comprises, =a-pair of substantially identical half-portions for embracing opposite sides of a crankshaft-crankpin, each half portion comprising-a'yoke having opposed oppositely inclined contact surfaces for contacting the crankpin at -'cireumferential spaced portions thereof, securing means' carried byeach opposite yoke for engaging he -oth'er -ycike tosecure said yokes in diametrically opposite positions-on said crankpin,'- aligning meanscarried by each yoke slidably engageable with' the opposed yoke for preventing relative lateral movement of said yokes, screwmeans carried by each yoke for holding incremental weights upon the respective yokes, and nut means carried by said screw means for immovably securing said incremental weights to the respective yokes, the axis of said screw means on each yoke being in bisecting relationship to the angle formed by the inclined contact surfaces of said'yoke.

4. A r-bob weightzfor counterbalanced 'crankshafts of V-type eight cylinder internal combustion engines, which comprises, a pair' of substantially identical half-portions for embracing opposite sides of a crankshaft crankpin, each half-portion comprising a yoke having opposed oppositelyinclined contact surfaces' for' making line contact with the crankpin at circumferential spaced portions thereof, a cap screw carried by each opposite yoke for threadedly engaging the other yoke to secure said yokes in diametrically opposite positions on said crankpin, "dowelipins carried by "each yoke slidably engageable in 'aperturesiprovidedin "the opposed yoke for, preventing relative'latera-l movement of said yokes, means carried by each yoke for holding incremental weights 'upon' the respective yokes, L and removable securing means carried bysaid holding'means for rigidly securing 'saidincremental weights 'to the respective yokes.

F5. Abob'weightfor'counterbalanced crankshafts of an internalcombustionengine, which comprises, a pair of substantially identical half-portions for embracing oppositesides'of'a crankshaft crankpin, each half portion comprising-ayoke having'opposed divergently inclined planar-contact surfaces for making line contact with the crankpin-"atcircumferential spaced portions thereof, se-

. curing means carried 'byeach opposite yokefor engaging theo'ther yoke to secure saidyokes in diametrically opposite embracing positions on said crankpin, aligning means carried'bycach yoke slidably engageable with the opposed yoke forpreventing relative lateral movement of said yokes, a screw shank carriedby-each yoke, centrally apertured discweights removably threaded on each screw shank; andknurled wheel nut means threaded upon "each screw shankfor'securing said disc weights upon the respective yokes.

References Cited in the file of thispatent :UNITED STATES PATENTS 1,140,398 Buckingham Dec. 13, 1938 

